Automotive electronic systems, such as airbag systems, antilock brake systems (ABS) and passenger restraint systems often include electronic components that are physically distributed throughout the automobile. For example, an airbag system may contain an electronic control unit (ECU) coupled to one or more sensors, a driver circuit and an airbag. The driver is controlled by the ECU and may include a squib and a triggering element. When a sensor senses a sudden change in acceleration, it signals the ECU, which, in turn, signals the driver circuit to ignite the squib, thereby deploying the airbag.
The sensors are often located outside the ECU, often at relatively long distances, and may be connected to the ECU via several meters of wire. These wires are a significant cost factor in automotive systems and further contribute to the weight of the car. In order to minimize the weight and cost of the system, the number of wires used to connect a sensor to its corresponding ECU is often limited to the minimum of 2 lines. These lines are used to supply power to the sensor and to transmit the data back to the ECU by modulating the current consumption of the sensor. Example interfaces that support operation in the manner are the Peripheral Sensor Interface PSIS, and the Digital Sensor Interface (DSI), which are both intended for the use in automotive airbag or powertrain systems. Other examples include the pulsewidth modulation (PWM) based protocols used by the Infineon TLE4941 and TLE4942 ABS wheel speed sensors, and by the ABS sensor protocol described in European Patent Application No. EP 0 944 888 B1.
One issue of using long wires to connect sensors to the ECU is line resonance due to line inductance and capacitance. In some systems a RC filter may be placed between the interface of the sensor interface and the long wires used to connect the ECU with the sensor satellites in order to provide damping of the resonance between the line inductance and capacitors on the sensor side as well as on the ECU side and to attenuate injected EMC. In other systems, ringing due to resonance is attenuated by actively controlling the line voltage using a control loop.